signTransaction.java

progressTracker.setCurrentStep(TX_SIGNING);

// We finalise the transaction by signing it,
// converting it into a ``SignedTransaction``.
SignedTransaction onceSignedTx = getServiceHub().signInitialTransaction(txBuilder);

// We can also sign the transaction using a different public key:
PartyAndCertificate otherIdentity = getServiceHub().getKeyManagementService().freshKeyAndCert(getOurIdentityAndCert(), false);
SignedTransaction onceSignedTx2 = getServiceHub().signInitialTransaction(txBuilder, otherIdentity.getOwningKey());

// If instead this was a ``SignedTransaction`` that we'd received
// from a counterparty and we needed to sign it, we would add our
// signature using:
SignedTransaction twiceSignedTx = getServiceHub().addSignature(onceSignedTx);

// Or, if we wanted to use a different public key:
PartyAndCertificate otherIdentity2 = getServiceHub().getKeyManagementService().freshKeyAndCert(getOurIdentityAndCert(), false);
SignedTransaction twiceSignedTx2 = getServiceHub().addSignature(onceSignedTx, otherIdentity2.getOwningKey());

// We can also generate a signature over the transaction without
// adding it to the transaction itself. We may do this when
// sending just the signature in a flow instead of returning the
// entire transaction with our signature. This way, the receiving
// node does not need to check we haven't changed anything in the
// transaction.
TransactionSignature sig = getServiceHub().createSignature(onceSignedTx);
// And again, if we wanted to use a different public key:
TransactionSignature sig2 = getServiceHub().createSignature(onceSignedTx, otherIdentity2.getOwningKey());